Conventionally, radio tomographic imaging and displaying systems are widely used in clinical practice. In such a radio tomographic imaging and displaying system, a radiation source and a radiographic image detector are disposed to face each other via a subject, and the set of the radiation source and the radiographic image detector are made to orbit around the subject to take radiographic images with applying radiation from various angles, and a tomographic image is reconstructed using the radiographic images taken at the individual angles to display an arbitrary slice.
An example of a method for reconstructing a tomographic image for use with the above-described radio tomographic imaging and displaying system is a successive approximation process, where linear absorption coefficients in a slice are modeled with a matrix and solved using a statistical way of thinking.
The successive approximation process is a reconstruction method where a tomographic image of interest is obtained by repeating an iteration based on radiographic images taken at individual imaging angles. Reconstruction methods which are usually referred to as an algebraic approach or statistical approach fall under the successive approximation process, and examples thereof include the ML-EM (Maximum Likelihood—Expectation Maximization) method and the OS-EM (Ordered Subsets Expectation Maximization) method.